President Donald Trump is on his way to Asia for a 10-day trip. For the moment, he has left behind a swirling investigation of Russia's interference in last year's election. The president shared some parting thoughts about the special counsel's probe before he boarded a helicopter this morning.

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PRESIDENT DONALD TRUMP: All I can tell you is this. There was no collusion. There was no nothing. It's a disgrace frankly that they continue.

SHAPIRO: His remarks capped a remarkable 24 hours in which he seemed to attack his own Justice Department once again. And joining us to talk more about this is NPR's Carrie Johnson. Welcome back.

CARRIE JOHNSON, BYLINE: Hi, Ari.

SHAPIRO: Explain the president's concerns about his own Department of Justice.

JOHNSON: Well, it was a bad week for the president when it comes to the law. Remember; starting on Monday, the first indictments came out in the special counsel investigation targeting Trump's former campaign chairman Paul Manafort and his deputy. Then there was the surprise guilty plea by a foreign policy aide in the Trump campaign.

That aide, George Papadopoulos, said he proposed a meeting between Trump and Vladimir Putin in a meeting with candidate Trump in March 2016. The aide said Senator Jeff Sessions, who's now the Attorney General, was at that meeting, too. That's a whole new avenue for the criminal investigation that's focusing on the highest levels of the government. And today Donald Trump said, I don't remember much about that meeting. He called it very unimportant. Sessions says he doesn't remember it either.

SHAPIRO: The president was also asked before he left today whether he would fire his attorney general and he said, I don't know. Certainly Democrats have had concerns about the attorney general but a different set of concerns. What's going on here?

JOHNSON: Well, the president's been ranting about Jeff Sessions on and off ever since Sessions recused himself from the Russia investigation and the Justice Department named a special counsel to look into those allegations. Trump said today he was very disappointed in the Justice Department, and in an interview with the station WMAL on Thursday, Trump openly talked about his frustration. Let's take a listen.

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TRUMP: You know, the saddest thing is that because I'm the president of the United States, I am not supposed to be involved with the Justice Department. I'm not supposed to be involved with the FBI. I'm not supposed to be doing the kind of things that I would love to be doing. And I'm very frustrated by it.

SHAPIRO: What would he love to be doing, Carrie?

JOHNSON: Well, fortunately we have some tweets to explain Donald Trump's state of mind. The president has tweeted he wants the Justice Department to investigate his political opponent Hillary Clinton and other Democrats. The president's still angry at James Comey. That's the FBI director he fired under questionable circumstances in May. And today, this afternoon, the president said he was unhappy about the sentence a military court gave service member Bowe Bergdahl for deserting his post in Afghanistan. Bergdahl got no prison time. The president tweeted that punishment was a, quote, "complete and total disgrace."

SHAPIRO: And we're going to hear more about that case elsewhere in the program. But these tweets go to some basic fundamental principles about how the American system is supposed to work - the independence of the judiciary, the wall that is supposed to exist between the Department of Justice and politics. Is that wall eroding?

JOHNSON: Well, Trump has said and done quite a few things this year to breach that wall. Remember; he asked the Justice Department to drop a case against his supporter, former Sheriff Joe Arpaio in Arizona. He repeated demands that the FBI investigate Hillary Clinton, and he's been beating up on the FBI and the intelligence community which he called Nazis earlier this year.

But it's important to know the Justice Department did not drop that case against Sheriff Arpaio. The matter ended only when the president pardoned him, and there is no public sign the Justice Department has reopened any investigation of Hillary Clinton. Now, sources tell me people at the DOJ and the FBI are not happy to wake up every morning to these mean tweets from the White House, but they're continuing to do their jobs. The question is, how long can these institutional checks and balances, this wall of independence stand firm?